Modern machining technology development focuses largely on enhancing the reliability, efficiency, and precision in material removal processes. It is now clearly recognized that the dynamic stiffness properties of the machine tools and the tools themselves play an extremely important role in the general performance of such processes.
Dynamic stiffness as a structural property is also of paramount importance in various kinds of vehicles and the components thereof. An example includes aircraft engines and their attachment to the wings, where a correct adjustment of the dynamic stiffness results in reduction of noise in the cabin area, see Jesse De Pries, “Aircraft Engine Attachment and Vibration Control”, Lord Corporation, Lord Library of Technical Articles, LL-6505, U.S. Pat. No. 6,102,664 and U.S. published patent application 2006/0060696.
Dynamic stiffness plays in fact a role in a much wider range of applications, for example in sports hardware, see U.S. Pat. No. 5,176,868, computer hardware, see U.S. published patent application 2003/0198157, and in space exploration, see the Japanese published patent applications 2004074906 and JP 57151046.
When machining work pieces through material removal, high dynamic stiffness helps to obtain high dimensional precision and fine surface finish. High dynamic stiffness also promotes longer machine and tool lifetime, increased reliability, and improves the environment. Numerous recently published patents protect the ongoing development in this area, see in particular U.S. Pat. No. 3,692,370, European published patent application 1008408, Canadian patent 1073954 and European published patent application 0860232.
The currently used methods for enhancing dynamic stiffness of the machines are based on the three different approaches or a combination of thereof. These are structural improvement of the machine design, which is often both difficult and costly, use of materials having a high damping capacity in the machine parts themselves, see U.S. Pat. Nos. 6,901,914 and 5,239,886, and separation of the machine parts by layers of a damping material, see U.S. Pat. No. 6,102,664.
Hence, there is a high demand for new efficient materials that increase the dynamic stiffness of machines, and subsequently there is continuous development of new materials, see U.S. Pat. No. 6,059,533 and Japanese published patent application 2004291408. An analysis of recent patents and related publications shows that these are materials mainly are based on resin or viscoelastic polymers such as in the cited Japanese patent application 2004291408. Another kind of composite materials includes materials comprising fillers, see U.S. Pat. No. 5,965,249. Among these materials the perhaps most promising class is carbon nanoparticle reinforced composites. By adding carbon nanoparticles it is possible to significantly increase the dynamic stiffness of polymers, metals, and concrete, see X. Zhou et al., “Interfacial damping characteristic of carbon nanotube-based composites”, Composites Science and Technology, Vol. 64, 2004, pp. 2425-2437, and Mark D. Frogley et al., “Mechanical properties of carbon nanoparticle-reinforced elastomers”, Composites Science and Technology, Vol. 63, 2003, pp. 1647-1654. It has been shown that the stiffness of polymers can be enhanced 2-3 times by imbedding carbon nanoparticles in polymers. It is also been shown that the damping capacity of polymers can be significantly enhanced by the same method.
Another example is Cu based alloys, see the Russian patent 2224039, that when enhanced by carbon nanoparticles render a stiffness that is about 1.4-1.5 times higher than that of ordinary copper and increases the static stiffness to levels comparable with that of beryllium brass. It is a well known fact that beryllium brass is the strongest copper based alloy and is used for manufacturing of springs having a high spring stiffness. A high static stiffness together with high damping capacity is required for achieving of a high dynamic stiffness.
However, these known materials and the processes for manufacturing them have a number of serious drawbacks.
The drawbacks of polymer based composites, on one hand, are poor tribological properties, limited operating temperatures, less than 100° C., and they exhibit the natural tendency of polymers to degrade in time. In addition, the damping capacity of these materials is strongly dependent on operational temperature and frequency. On the other hand, the production of carbon nanoparticles reinforced metal composites is faced with the problem of carbon oxidation, i.e. “combustion”, during the process of mixing the particles into the melted metal. Therefore, it can be said that there at present are no industrially scalable processes for manufacturing high dynamic stiffness materials.
Nanocomposite materials having an non-polymer matrix material and enhanced mechanical characteristics are disclosed in A. Goyal et al., “Enhanced yield strength in iron nanocomposite with in situ grown single-wall carbon nanotubes”, J. Mater. Res., Vol. 21, No. 2, Feb. 2006, pp. 523-528. Single wall nanotubes were grown in a porous iron material using acetate precursors.
A composite material comprising carbon nanotubes disposed in a metal matrix is disclosed in published U.S. patent application 2004/0266065 for Zhang et al. The material is formed by first growing nanotubes on a substrate using CVD processes and catalysts. In the CVD precursors such as methane, ethylene and acetylene can be used. The substrate has to be heated to relatively high temperatures such as at least 700° in the processes. A layer of metal is then deposited over the carbon nanotubes using methods such as electroplating, electroless plating, sputtering and CVD.